Line marking apparatus

ABSTRACT

An apparatus for line marking a sheet. Means are provided for marking lines on a sheet which includes a rotatably mounted line inscribing means having a line printer and an inker. Additional means are provided for driving the sheet to be marked past the line marking means. The line printer is provided with one marking surface per line and is rotatably mounted in cooperative relation with the inker and the driving means so as to be inked by the former and substantially driven by the latter. The sheet is inkmarked with lines by the printer as it is driven past the printer. The location of a marked line on the sheet as well as the spacing between marked lines if more than one is inscribed, can be varied by changing the lateral position of the printer marker surfaces with respect to the sheet to be marked and/or each other. The marking means is provided with a variable means for adjusting the contact pressure between the line printer, the sheet to be marked, and the driving means.

United States Patent 1 1 Leri 1 Jan. 2, 1973 [541 LINE MARKING APPARATUS [76] lnventor: Mario Leri, 77 Seventh Avenue, Primary Examiner-John Mclnyosh New York NY 001 1 Attorney-Hubbell, Cohen and St1efel [22] Filed: May 28, 1970 [57] ABSTRACT [21] Appl. No.: 41,451 An apparatus for line marking a sheet. Means are provided for marking lines on a sheet which includes a rotatably mounted line inscribing means having a line [52] US. Cl. ..118/l, 118/222, 118/241, primer and an inker Additional means are provided 118/249 118/252 118/262 for driving the sheet to be marked past the line mark- [51] 1111. C1. ..B05c 1/03, B056 1/16 ing means The line printer is provided with one mark [58] Fleld of Search ..118/1, 2, 221, 222, 241, 252, m surface per line and is rotatably mounted in 11850512491262 cooperative relation with the inker and the driving means so as to be inked by the former and substan- 1 References Cited tially driven by the latter. The sheet is ink-marked with lines by the printer as it is driven past the printer. UNITED STATES PATENTS The location of a marked line on the sheet as well as 1,439,464 12/1922 Bowersock ..118/262 the Spacing between marked lines if more than one is 3,534,681 10/1970 B61118 et al. ..11s/249 x cr e can be varied by changing the lateral posi- 2,625,085 1/1953 Bergstein .,118/222 x tion of the printer marker surfaces with respect to the 1,549,273 8/1925 Lee ..118/251 X sheet to be marked and/or each other. The marking 2,557,696 6/1951 Schaefer.., ..118/1 means is provided with a variable means for adjusting 3,343,519 l0/1967 W et the contact pressure between the line printer, the 2,590,339 3/1952 Minkow "1 heet to be marked and the driving means 2,614,522 10/1952 Snyder ..l'l8/1 UX 2,925,064 2/1960 Kahn ..118/505 11 Claims, 3 Drawing Figures PATENTH] JAN 2 7 I I I V J J r- I 5 INVENTOR MARIO LERI WMM ATTORNEYS.

LINE MARKING APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for marking lines on a sheet in which the marking means cooperates with a driving means to mark lines on the sheet as it is driven past the marking means.

2. Description of the Prior Art The prior art method and apparatus for marking lines on a sheet, such as a planar sheet, requires either the production of a printing plate or the use of a hand operated roller and separate ink pad. In the instance where a printing plate is utilized, the length of the lines to be marked is fixed and a new plate must be utilized each time a new line length is desired. In the instance where a hand operated roller and separate ink pad are utilized, the accuracy of the location of the lines can not be assured for a single line marking operation or a plurality of successive line marking operations wherein identical line locations are desired. These deficiencies become particularly acute when it is desired to make printing masters for use in photo-offset printing, or in other instances where the location of the lines is critical.

In photo-offset printing, it is customary. to prepare a master sheet containing the information to be reproduced such as, for example, type or illustrations or the like. In making this master sheet, it is desirable to provide it with markings to define the borders or margins of the sheet and the center lines. Other guide lines may also be defined. In addition, it is essential to provide such a master sheet with markings defining so called trim lines.

Once the master sheet is marked, it is provided with the desired indicia and is then photographed to reproduce what is commonly termed a photo-offset master. It is commonly desirable that the photo-offset master not contain the guide lines such as the margin lines or the center lines, etc. However, it is desirable that the photo-offset master contain the trim lines. To affect this differential, it is known to provide the master sheet from which the photo-offset master is photographed with the guide lines in an ink of a color that will not photo reproduce, whereas the trim lines are provided in a color that will photo reproduce. For example, with standard films used in photo-offset printing, the guide lines are marked in blue, which is a so called non-photographic ink and the trim lines are marked in red, which is a so called photographic ink and will reproduce.

I-Ieretofore, great difficulty has been encountered in printing lines of different colors on the same sheet simultaneously. This problem of simultaneous multicolor printing is one that is solved by the present invention. Secondly, in marking master sheets from which photo-offset masters are made, there has not been sufficient flexibility in marking masters sheets of different widths or lengths. Heretofore, such variations in dimensions have required time consuming adjustment in marking apparatus which is costly. This problem is also solved by the present invention.

SUMMARY OF THE INVENTION An apparatus for line marking a sheet is constructed which includes means for marking a line on the sheet,

the marking means including a rotatably mounted line inscribing means. In addition means are provided for driving the sheet past the marking means. The line inscribing means is rotatably mounted in cooperative relation with the driving means to be substantially driven by the driving means whereby the sheet is line marked as it is driven past the line inscribing means. The line inscribing means includes a rotatably mounted inking means and a line printing means. The line printing means is rotatably mounted in cooperative relation with the inking means and the driving means so as to be inked by the former and substantially driven by the latter. In addition means for maintaining a contact pressure between the line inscribing means, the sheet to be marked and the driving means is provided, wherein the contact pressure means includes means for varying the contact pressure.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the preferred embodiment of the present invention;

FIG. 2 is an enlarged fragmentary view of the embodiment shown in FIG. 1 taken along line 2-2 partially in section and partially in schematic; and

FIG. 3 is a plan view of a line marked sheet produced utilizing the embodiment shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, and particularly to FIG. 1, the line marking apparatus, generally designated by the reference numeral 10, includes a platform or base 12. The base 12, across which a sheet 14 to be marked is driven, is preferably formed of a material having ferromagnetic properties at the portion of the base 12 which the sheet 14 is driven across, for a purpose to be described in greater detail hereinafter. A pair of longitudinally extending spaced apart parallel guides 16 and 18 for the sheet 14 are mounted on the platform 12. Preferably, at least one of the guides 18 is movably mounted on platform 12 and is positionable at a plurality of different spacings from guide 16, to accommodate different widths of sheet 14. The movable guide 18 preferably includes a magnet at the portion thereof which is in contact with the ferromagnetic portion of the base 12 so as to releasably retain the guide 18 on the base 12. The base 12, preferably, has an opening 19 at one end thereof, through which a driving roller 38 protrudes so as to contact the underside of the sheet 14, which is the opposite side from the side to be marked, and cooperate in driving the sheet 14 across the base 12 in a manner to be described in greater detail hereinafter.

The drive roller 38 is located below base 12, and extends transversely of the guides 16 and 18. The drive roller 38, as shown and preferred, is driven by means of a motor 40 and a pulley 42-44, and belt 46 arrangement. The motor 40 is preferably provided with a rheostat 48 for setting the speed of the motor 40 to any desired rate. The rheostat 48 is connected between the motor 40 and the power source 50, shown illustratively as an AC power source.

A guide rod 22 is mounted on the base 12 next to the opening 13 and is coextensive with the drive roller 38. The guide rod 22 preferably extends substantially parallel to the longitudinal axis of the drive roller 38 for its full length. The guide rod 22 is preferably notched along its length, on opposite sides so as to provide a plurality of equi-size notch pairs 24 which are, preferably, spaced apart from each other by a common predetermined measurement interval dependent on the number of lateral positions along rod 22 in which it is desired to mark lines. A line marking means, illustratively shown as comprising five line marking devices 26, 28, 30, 32 and 34 is removably mounted on the guide rod 22 each in a particular notch pair 24 dependent on its desired marking position so as to each be laterally adjustable along the length of the guide rod 22 to a new marking position in either lateral direction, as indicated by the arrow 36. Switching means, which are preferably monostable spring-loaded micro switches 52 and 54 having a stable open position, are mounted on the platform 12 on either side of the opening 13, preferably as close to the drive roller 38 as possible, and are electrically connected in series (FIG. 2) with a source of power 55, illustratively shown as being an AC power source, and an electromagnet 57, which is mounted on the base 12 in cooperative relationship with the line marking devices 26, 28, 30, 32 and 34, so as to form an energizing circuit for electromagnet 57 and control the energization thereof. The electromagnet 57 controls the operative engagement of the line marking devices 26, 28, 30, 32 and 34 with the driving roller 38 in a manner to be described in greater detail hereinafter. The opening 13 (FIG. 2) is preferably smaller at the uppermost extremity than the lowermost extremity, so that a large drive roller 38 can be accommodated in the opening 13 for driving the sheet to be marked 14, in a manner to be described in greater detail hereinafter, while providing a minimum spacing between the switches 52 and 54.

The presently preferred form of line marking device 30 is shown in greater detail in FIG. 2. Preferably, line marking devices 26, 28, 32 and 34, are identical with line marking device 30, which will now be described in detail. The line marking device 30 includes a housing generally referred to by the reference numeral 56 having a front portion 58 and a rear, or base portion 60. The front housing portion 58 is pivotally connected to the base portion 60 by means of pin 62 so as to pivot at a point 64 in the directions indicated by the arrow 66. The base portion 60 of the housing 56 is further secured to the front portion 58 of the housing 56 by a resilient member, illustratively shown as a tension spring 68, which preferably has a tendency to urge the front portion 58 of the housing 56 to pivot about the point 64 in the direction indicated by the arrow 70.

In addition to pivot pin 62 and spring 68, the base portion of the housing 56 is secured to the front portion 58 of the housing 56', preferably by means of a threaded screw-member 72 which is an adjustable stop, so as to permit the front portion 58 of the housing 56 to be pivoted in either direction to a new fixed rest position determined by the threaded position of the screw 72. The adjustable stop 72, preferably, has a compression spring 73 mounted in i surrounding relation therewith which has a tendency to urge the front housing portion 5 8 forward so as to have a tendency to pivot about point 64 in the direction indicated by the arrow and urge line printing roller 84 into operative engagement with the drive roller 38. The tension on the spring 73 is preferably adjusted by means of threading screw 72 to a point such that when the front housing portion 58 is forward in the operative driving position, the printing roller 84 will be pressed against drive roller 38 with a substantial force in order to leave a well defined line as will be described.

Base portion 60 of the housing 56 is preferably formed with a slot 74 at the bottom portion 71 thereof and an aperture 78 normal to the slot 74 and in communication therewith. Preferably, the width of the slot 74 is substantially equivalent to the width of one of the notches 24 of the guide rod 22 and the depth of the central portion of the rod 22. Another screw-like member 76 is threaded through the aperture 78 so as to bear against the guide rod 22 at the central portion 23 thereof when base portion 60 is positioned on the guide rod 22 in a notch pair 24 with the guide rod central portion 23 being situated in the slot 74. Thus, device 30 is adjustably positionable on rod 22 and is releasably lockable in any chosen position by screw 76.

The front housing portion 58 is preferably formed with a guideway 80 which is preferably angularly disposed on the sides of the front housing portion 58, for a purpose to be described in greater detail hereinafter- The line inscribing means, which preferably includes inking roller 82 and line printing roller 84, is rotatably mounted in the front housing portion 58. The inking roller 82 is rotatably mounted in the downwardly slanted guideway 80 and is freely slidable therein. Due to the force of gravity, inking roller 82 is urged toward the bottom of guideway 80. The inking roller 82 may preferably be of the dry ink roller type manufactured by the Johnson Wax Company and disclosed in the US. Pat. No. 2,777,824. Such a roller has an ink containing portion 94 sandwiched between two outer circular members which are larger in diameter than the ink containing portion 94 so as to form a guideway therebetween. This dry ink roller 82may be any desired ink color, as will be explained in greater detail hereinafter.

The line printing roller 84 preferably has an outer surface 86 whose thickness is equivalent to the width of a line to be drawn. Preferably, the line printing roller 84 is rotatably mounted in a fixed position in the front housing portion 58. The line printing roller 84 is preferably positioned so that it contacts the drive roller 38 along a line 88 normal to the sheet 14. Furthermore, the line printing roller 84 is positioned in the front housing portion 58 in cooperative relation with the ink roller 82 so as to have the surface 86 disposed in the guideway 95 in engagement with the ink containing portion 94 of dry ink roller 82 when the printing roller 84 is engaged by ink roller 82. The front housing portion 58 is preferably formed with a ferromagnetic material along the bottom portion thereof next to the rear most edge 102 of the opening 13. The ferromagnetic portion 100 of the front housing portion 58 is positioned opposite the electromagnet 57 so as to be magnetically attracted thereby, for a purpose to be described in greater detail.

OPERATION Now describing the operation of the line marking apparatus 10 in greater detail. The sheet 14, which may be a piece of paper utilized as a photo-offset printing master sheet, is inserted on the platform 12. The movable guide 18 is preferably adjusted so that the paper 14 just fits in sliding engagement between the guide 16 and 18. The line marking devices 26, 28, 30, 32, and 34 are laterally positioned on the guide rod 22 in the desired locations defined by slots 24 and corresponding to particular defined positions so as to each mark a line 108, 110, 112, 114, and 116, respectively, in a desired position upon the sheet 14, and are locked in those positions by operation of lock screws 76. The color of these lines is dependent upon the color of the dry ink roller ink containing portion 94. Preferably, for a photo-offset printing master in which guide lines and trim lines are desired, a trim line which may be represented by lines 108 and 116 may be drawn in photographic red ink while the guide lines represented by lines 110, 112 and l 14 are drawn in non-photographic blue ink.

The motor 40 is turned on and the drive roller 38 begins to rotate in accordance with the belt 46 and pulley arrangement 42-44. The sheet 14 is thenurged forward by conventional means, such as by hand, so as to close the first micro-switch 52, at which time the front housing portion 58 is still held out of operative engagement with the drive roller 38 by means of spring tension due to spring 68. The sheet 14 is continued forward by the drive roller 38 until micro-switch 54 is closed. This completes the series circuit between the power source 55 and the electromagnet 57 causing a current to flow through the electromagnet 57 and which energizes the electromagnet 57 so as to create a surrounding electromagnetic field. This electromagnetic field attracts the ferromagnetic portion 100 of the front housing portion 58 to the electromagnet 57 thus overcoming the tendency of spring 68, so as to place the line printing roller 84 in operative engagement with the driving roller 38.

The driving roller 38, which for purposes of illustration is rotating in the direction indicated by the arrow 118, drives the sheet 14 past the line printing roller 84 in the direction indicated by the arrow 120 due to the contact pressure engagement between the line printing roller 84 and the drive roller 38. As the sheet 14 is driven past the line printing roller 84, the line printing roller 84 is caused to rotate in the direction indicated by the arrow 122. The surface 86 of the line printing roller 84, which is engaged by the ink containing portion 94 of the dry ink roller 82, picks up ink from the ink containing portion 94 of the roller 82 which is caused to rotate in the direction indicated by the arrow 124, and which bears against the surface 86 of line printing roller 84 due to the force of gravity. In this manner ink is transferred from the ink containing portion 94 of the dry ink roller 82 to the line marking surface 86 of the line printing roller 84, which in turn marks a line on the sheet 14 thereby transferring the ink to the sheet 14. y

The sheet 14 is driven in the direction indicated by the arrow 120 past the line printing roller 84 until shortly before the end of the sheet 14 to be marked is reached. At this point the end of the sheet 14 has passed micro-switch 52 which is now opened due to no contact pressure being applied thereto, thus providing an open circuit between the power source 55 and'the electromagnet 57. Electromagnet 57 is no longer energized and an electromagnetic field is, therefore, no longer created. The tendency of the spring 68, therefore, cannot be overcome. The spring 68, therefore, urges the front housing portion 58 upward in the direction indicated by arrow 70, and the line printing roller 84 is brought out of the engagement with the drive roller 38. Therefore, no line is marked on the portion of the sheet 14 between the switch 52 and the point of tangential contact between the line printing roller 84 and the drive roller 38. The momentum of the sheet 14 is such as to carry the sheet 14 past the drive roller 38 so that the sheet 14 may be collected for use.

Because of the control action of micro-switches 52 and 54 in placing the line printing roller 84 in operative engagement with the drive roller 38 only after both switches 52 and 54 are closed, no line is marked on the sheet 14 at the beginning of'the sheet 14 in the distance between the point of tangential engagement between line printing roller 84 and drive roller 38, and the switch 52. In this manner, bleeding of the ink at the ends of the sheet 14 is avoided. If bleeding is not a problem, or is not a concern, the anti-bleeding arrangement provided by spring 68, switches 52 and 54, electromagnet 57, power source 55, and ferromagnetic portion 100 may be omitted.

If it is desired to mark intersecting lines on the sheet 14, all that is required is that the sheet 14 be turned 90, the movable guide 18 be repositioned so as to accommodate the length of the sheet 14 (rather than its width), and the line marking devices 26, 28, 30, 32, 34 be laterally adjusted to the correct position. If fewer lines or more lines are desired, all that is'required is that one or more line marking devices, 26 through 34 inclusive, be added or omitted. A line marking device may be omitted merely by rotating the screw 76 so as to withdraw it frombearing relation with the guide rod '22 and lifting the housing 56 up. A device may be added by fixing the line marking device on the guide rod 22 and tightening the screw 76 to bring it in bearing relation with the guide rod 22.

By utilizing the present invention a simple and efficient means for marking lines on a sheet, such as to prepare a photo-offset printing master, is provided which is flexible, economical, and rapid so that aplurality of identically marked sheets can be produced rapidly and efficiently, or a plurality of differently lined marked sheets can be produced in an economical and relatively simple manner. 1

As used herein throughout the specification the term sheet" is not limited to anobject having planar surfaces, but encompasses an object having any geometric shape surface on which a line may be marked.

it is to be understood that the above described em bodiment of the invention is merely illustrative of the principles thereof and that numerous modifications and embodiments of the invention may be derived within the spirit and scope thereof, such as by replacing the individual line marking devices, each having a separate ink roller and a separate line printing roller, with a single device which comprises a single ink roller extending along the length of the drive roller 38 and a single line roller having a plurality of line marking surfaces, each line marking surface being located at a desired line marking position.

What is claimed is: I

1. An apparatus for line marking a sheet comprising:

a plurality of means for marking at least an equal plurality of lines on said sheet, each of said line marking means including a housing, a dry inking means, a line printing means, and a guideway for said inking means, said inking means including means for rotatably mounting said inking means in said guideway, said inking means rotatable mounting means being freely mounted in said guideway for freely mounting said inking means in said guideway, said guideway being disposed in said housing for placing said rotatable inking means in cooperative driving relationship with said line printing means due to said free mounting of said inking means, means for driving said sheet past said plurality of marking means, said driving means including a positively driven drive roller means, said sheet being driven between said drive roller and said line printing means, said line printing means being rotatably mounted in said housing in cooperative relation with said inking means and being disposed with respect to said drive roller means in cooperative driving relationship therewith and being maintained in said driving relationship due to contact pressure between said driving roller means and the line printing means, said line printing means being inked by the inking means and substantially driven by the driving roller means due to the contact pressure therebetween, said driven line printing means driving said inking means whereby said line printing means is inked and the sheet is line marked as it is driven past said plurality of line printing means, and

guide means, each of said marking means being removably mounted on said guide means to be individually laterally positionable along said guide to a desired operating line marking position, said positions being laterally variable whereby the spacing between said plurality of lines may be varied.

2. An apparatus in accordance with claim 1, further comprising:

means mounted in cooperative relation with said plurality of marking means for guiding said sheet past said marking means.

3. An apparatus in accordance with claim 2, wherein:

said guiding means includes a first guide and a second guide spaced apart from said first guide, said second guide being movably mountedand positionable at a plurality of different spacings from said first guide.

4. An apparatus in accordance with claim 3, wherein said second guide includes a magnet and said apparatus includes a platform across which said sheet is driven, said platform having ferromagnetic properties and said second guide being movably mounted on said platform.

' 5. An apparatus in accordance with claim 1, wherein sheet. 7. An apparatus in accordance wlth claim 9, wherein each of said housings includes a first portion which includes said line printing means and said inking means, and a second portion, said first portion being pivotally connected to said second portion.

8. An apparatus in accordance with claim 7, wherein said pressure maintaining means includes a resilient means operatively connected between said housing portions, said pressure means further including means for varying theresilient loading of said resilient means whereby as said resilient load is varied said first portion is pivoted in relation to said second portion from a first rest position to a second rest position.

9. An apparatus in accordance with claim 1, wherein:

each of said marking means includes means for sensing the position of the sheet with respect to the driving means and controlling the position of the line printing means with respect to the driving means so as toline mark the surface only during a desired interval.

10. An apparatus in accordance with claim 9, wherein:

said sensing means includes first and second switching means disposed before and after said driving means point of sheet drive, said line printing means not being in cooperative relation with said driving means so as not to be driven thereby and out of contact with said sheets when either of said switching means is open.

11. An apparatus in accordance with claim 10, wherein:

each of said marking means includes a ferromagnetic portion and a resilient means having a tendency to urge the line printing means away from said driving means and out of contact with said sheet;

a power source; and

said sensing and controlling means includes an electromagnet positioned in cooperative relation with said marking means ferromagnetic portion and connected in series with said power source and said first and second switching means, the force executed on said marking means by said electromagnet overcoming the tendency of said resilient means and urging the line printing means into substantial driving engagement and in contact with said sheet. 

1. An apparatus for line marking a sheet comprising: a plurality of means for marking at least an equal plurality of lines on said sheet, each of said line marking means including a housing, a dry inking means, a line printing means, and a guideway for said inking means, said inking means including means for rotatably mounting said inking means in said guideway, said inking means rotatable mounting means being freely mounted in said guideway for freely mounting said inking means in said guideway, said guideway being disposed in said housing for placing said rotatable inking means in cooperative driving relationship with said line printing means due to said free mounting of said inking means, means for driving said sheet past said plurality of marking means, said driving means including a positively driven drive roller means, said sheet being driven between said drive roller and said line printing means, said line printing means being rotatably mounted in said housing in cooperative relation with said inking means and being disposed with respect to said drive roller means in cooperative driving relationship therewith and being maintained in said driving relationship due to contact pressure between said driving roller means and the line printing means, said line printing means being inked by the inking means and substantially driven by the driving roller means due to the contact pressure therebetween, said driven line printing means driving said inking means whereby said line printing means is inked and the sheet is line marked as it is driven past said plurality of line printing means, and guide means, each of said marking means being removably mounted on said guide means to be individually laterally positionable along said guide to a desired operating line marking position, said positions being laterally variable whereby the spacing between said plurality of lines may be varied.
 2. An apparatus in accordance with claim 1, further comprising: means mounted in cooperative relation with said plurality of marking means for guiding said sheet past said marking means.
 3. An apparatus in accordance with claim 2, wherein: said guiding meaNs includes a first guide and a second guide spaced apart from said first guide, said second guide being movably mounted and positionable at a plurality of different spacings from said first guide.
 4. An apparatus in accordance with claim 3, wherein said second guide includes a magnet and said apparatus includes a platform across which said sheet is driven, said platform having ferromagnetic properties and said second guide being movably mounted on said platform.
 5. An apparatus in accordance with claim 1, wherein said guideway is an angularly disposed slot in said housing.
 6. An apparatus in accordance with claim 1, wherein: each of said marking means includes means for maintaining said contact pressure between said line printing means, said sheet and said driving means for enabling said line printing means to mark said sheet.
 7. An apparatus in accordance with claim 9, wherein each of said housings includes a first portion which includes said line printing means and said inking means, and a second portion, said first portion being pivotally connected to said second portion.
 8. An apparatus in accordance with claim 7, wherein said pressure maintaining means includes a resilient means operatively connected between said housing portions, said pressure means further including means for varying the resilient loading of said resilient means whereby as said resilient load is varied said first portion is pivoted in relation to said second portion from a first rest position to a second rest position.
 9. An apparatus in accordance with claim 1, wherein: each of said marking means includes means for sensing the position of the sheet with respect to the driving means and controlling the position of the line printing means with respect to the driving means so as to line mark the surface only during a desired interval.
 10. An apparatus in accordance with claim 9, wherein: said sensing means includes first and second switching means disposed before and after said driving means point of sheet drive, said line printing means not being in cooperative relation with said driving means so as not to be driven thereby and out of contact with said sheets when either of said switching means is open.
 11. An apparatus in accordance with claim 10, wherein: each of said marking means includes a ferromagnetic portion and a resilient means having a tendency to urge the line printing means away from said driving means and out of contact with said sheet; a power source; and said sensing and controlling means includes an electromagnet positioned in cooperative relation with said marking means ferromagnetic portion and connected in series with said power source and said first and second switching means, the force executed on said marking means by said electromagnet overcoming the tendency of said resilient means and urging the line printing means into substantial driving engagement and in contact with said sheet. 